Photolithography for manufacturing a semiconductor element, or the like, adopts an exposure apparatus which exposes a photosensitive substrate to the pattern image of a mask (e.g., a reticle) via a projection optical system. Recently, semiconductor integrated circuits have been developed toward micropatterning, and the wavelength of a photolithography light source is being decreased in photolithography.
Such an exposure apparatus suffers a decrease in the intensity of exposure light under the influence of absorption of exposure light by oxygen in the use of, as exposure light, vacuum ultraviolet rays, particularly, light with a wavelength shorter than 250 nm such as a KrF excimer laser beam (wavelength: 248 nm), an ArF excimer laser beam (wavelength: 193 nm), or an F2 laser beam (wavelength: 157 nm), harmonic light such as a YAG laser beam, or X-rays.
The prior art avoids a decrease in the transmittance of light as follows: a closed space which confines only an optical path is formed in an exposure apparatus having a light source such as an F2 excimer laser, and gas in the closed space is purged with gas such as nitrogen not containing oxygen.
FIG. 13 is a view showing an exposure apparatus which executes exposure by supplying inert gas into a space defined by an optical member on the final stage of a projection optical system (lens barrel) and a photosensitive substrate (wafer) and forming an inert gas atmosphere in the space. In this exposure apparatus, shielding members are arranged around the space in order to separate the space in the exposure region from an ambient atmosphere. Inert gas is supplied from the vicinity of the exposure region to the space.
The exposure apparatus shown in FIG. 13 requires several seconds until the oxygen concentration in the space in the exposure region decreases after a wafer stage is driven to load a wafer into the exposure region. This results in low throughput.
The same problem occurs when inert gas is supplied to the vicinity of a reticle. Also, for the reticle, the exposure apparatus requires several seconds until the oxygen concentration in a space surrounded by shielding members decreases, which decreases the throughput.